The present disclosure concerns a device to sample a web movement of a material web, a printing system that uses such a device, and a method to control a handling process.
Printing systems to print web-shaped recording material have long been known. Such printing systems normally have a device to scan the web movement. These devices typically comprise a free-wheeling roller that is in contact with the web-shaped recording material and translates the linear motion of the recording material into a rotary motion. The roller is coupled to an incremental encoder. The incremental encoder translates the rotary motion of the roller into a (normally electrical) control signal. Different types of incremental encoders are known. On the one hand, they differ in the manner of sampling. There are thus incremental encoders that photoelectrically scan the line pattern applied on a disc. There are incremental encoders that sample a rotating magnetic pattern and which operate by means of slip contacts. There are even incremental encoders that output a directional signal. Such incremental encoders generate two phase-offset output signals that are translated via a corresponding post-processing into a movement signal and a direction signal. Alternatively, the two phase-offset output signals can also be converted by means of commercially available quadrature decoders into one signal that is only generated given movement in one direction and into an additional signal that is generated only given movement in the other direction.
The movement of a web-shaped material web can be sampled with such incremental encoders. These incremental encoders are used to sample the motion of a web-shaped recording material in printing systems. However, they are also used to sample the motion of other material webs and conveyor belts in production facilities.
In principle, in printing systems and in production systems there exists the need to increase the speed of the web movement. The higher the rated speed of a web, the more complicated the activation or deactivation of the corresponding system since such a web must be accelerated gradually up to the rated speed upon activation and must be braked gradually upon deactivation. The control of the speed of the web takes place by means of a control signal provided by a central control device, which control signal is typically a digital, pulsed signal. This signal provides the speed of the web. Since the movement of the web is subject to a significant inertia of the material and of the rollers that are in contact with this, the actual speed of the web deviates from the speed provided by the control signal often markedly from the desired speed, primarily upon running up and braking the web.
Since the additional processes that are connected with the web speed—for example the printing of the web shaped recording material or other handling and processing processes of a material web—are also controlled by means of the control signal output by the central control device, the production or the printing process is normally deactivated upon acceleration or upon braking of the web. Spoilage of unprocessed material web (recording material) is hereby generated, what is known as maculature. The higher the rated speed of the material web, the longer that the run-up or braking of the material web takes, and the larger the corresponding quantity of maculature as well.